It is known from German Pat. No. 1,182,414 to make bags from a multilayer thermoplastic strip workpiece, normally of polyethylene, in an apparatus having transport means for conveying the workpiece longitudinally in a transport direction along a path underneath an upper welding element having relative to the direction an upper upstream welding tool extending across the path and generally parallel thereto an upper downstream welding tool. Respective lower upstream and downstream welding tools are vertically aligned with the upper upstream and downstream tools and a blade extends transverse to the path between one of the upstream tools and the respective downstream tool. The upper and lower tools with the workpiece between them are relatively displaced toward one another to weld the workpiece together along upstream and downstream seams at the respective tools and to cut the workpiece across with the blade between the seams, and away from one another to free the severed downstream end section of the workpiece. Stacking means including a stack support downstream of the tools catches and holds the severed end sections in a stack.
Such an arrangement cannot normally conveniently be used other than double-seam operation, that is forming a pair of separate seams that are separated by the cut formed by the blade. In some situations it is preferable to form so-called bottom or end seams that extend wholly to the severed ends. This can be done in the above-described machine only by heating the blade and turning up the heat on the tools to form wide end seams. The result is a wide seam that wastes material and looks unattractive, while not being stronger than a preferred narrow bottom seam which can only be produced on a special-duty machine.
Stacking must normally be carried out downstream of the system, at least for double seaming. This further complicates use of the above-described machine for anything but a single use, since the differently seamed workpieces must be handled differently.